1. Field of the Invention
The present invention relates to a heat exchanger which constitutes a vehicle air conditioner. The present invention is based on Japanese Patent Application Nos. 11-201014, 11-219346, 11-220549, 11-220550, 11-220551, and 11-113111, the contents of which applications are incorporated herein by reference.
2. Description of the Prior Art
One example of the structure of a heat exchanger which is used as an evaporator in a vehicle air conditioner is shown in FIG. 25. This heat exchanger is known as a drawn cup type heat exchanger, which has becoming common recently and is configured so that a plate-shaped cooling medium flow portion 3 obtained by piling up substantially rectangular flat plates 1 and 2 which are subjected to drawing and cooling fins 4 bent into a wave shape are alternately laminated.
The flat plates 1 and 2 are brazed at the outer peripheral portions and the central portions in the cooling medium flow portion 3. As the result a U-shaped cooling medium flow path R which travels between a cooling medium inlet 5 provided at the upper portion and the lower portion and leads to a cooling medium outlet provided at the upper portion and is aligned parallel the cooling medium inlet 5, is formed within the cooling medium flow portion 3.
In this heat exchanger a cooling medium is distributed to each cooling flow portion 3 at the cooling medium inlet 5, and is vaporized in the process of passing through the cooling medium flow path R, and is then collected again at the cooling medium outlet 6. After that the collected cooling medium is discharged from the heat exchanger.
Incidentally, the following problems have been pointed for the above-mentioned structured heat exchanger.
(1) In a heat exchanger used as an evaporator, the dryness of the flowing cooling medium is not constant, but it gradually increases in the process of vaporization. Thus, for a flow path cross-sectional area along the direction of the cooling medium flow, the specific volume of the cooling medium is increased and the flow path resistance is increased as the cooling medium moves downstream of the flow path. Therefore, high heat conductivity cannot always be obtained in the entire heat exchanger under the present circumstances. Also pressure losses cannot always be controlled to small levels.
(2) The cooling medium inlet 5 forms a continuous space by laminating the cooling flow portion 3 as shown in FIG. 26. Thus, the cooling medium flowing into the heat exchanger is distributed to each cooling medium flow portion 3 in the process of flowing within this continuous space in the directions of the arrows in FIG. 26. However, in a conventional heat exchanger the cooling medium collectively flows into the cooling flow portion 3 positioned downstream in the direction of the flow of the cooling medium and the distribution of the cooling medium into each cooling medium flow portion 3 is not uniformly carried out. As a result, cooling medium is apt to stagnate, and in the cooling flow portion 3 positioned upstream side in the direction of the flow of the cooling medium, heat exchange is not sufficiently performed.
(3) The cooling medium flowing into the heat exchanger is distributed into each cooling medium flow portion 3 from a space formed by lamination of the cooling flow portions 3. However, since in the conventional heat exchanger the start portion of the cooling flow path leading to the space is narrower than the space, the cooling flow path R is rapidly reduced at this portion and pressure loss occurs. Also in the continuous space formed at the cooling medium outlet 6 the same phenomenon is occurs. That is, since the space formed at the cooling medium outlet 6 is wider than the end portion of the cooling flow path R, the cooling flow path R is rapidly enlarged at this portion and pressure loss occurs.
(4) The cooling medium flow portion 3 is formed by laminating two flat plates 1 and 2 which were subjected to drawing and brazing after providing the cooling medium portion R inside the plates. However, if the plates 1 and 2 are shifted, the disadvantage that airtightness of the cooling flow path R is not ensured or sufficient pressure resistance cannot be obtained or the like occurs. Thus, to prevent the shift of the flat plates 1 and 2, one of the flat plates is provided with a claw. And when the one flat plate is laminated with the other flat plate, this claw is closed to fix both flat plates. However, this shift prevention countermeasure has the problems that a step of closing the claw is needed thereby increasing the assembly time and excess material for the claw is needed whereby the production costs are increased when it is assumed mass production is used.
The present invention was made in consideration of the above-mentioned circumstances. It is an object of the present invention to reduce the pressure loss which acts on a cooling medium flow path in accordance with the change of dryness of the cooling medium thereby to enhance the heat exchange performance in a drawn cup type heat exchanger.
It is another object of the present invention to uniformly distribute a cooling medium to a cooling medium flow path and at the same time reduce the pressure loss in the cooling medium flow path thereby to enhance the heat exchange performance.
It is still another object of the present invention to review a shift prevention structure provided in two flat plates constituting a cooling medium flow portion thereby to reduce the assembly time and the production costs.